Various types of collision avoidance systems for vehicles have been proposed in the past, using various types of technologies, including ultrasonics, electro-optics and microwaves. Many of these systems are less than completely satisfactory for any of several reasons. Some of these systems, while quite effective in operation, are prohibitively expensive in terms of manufacturing costs to render them suitable for use on a widespread basis. Others suffer from operating deficiencies, including the tendency to yield an undue number of false detections or the failure to properly detect a vehicle or object which poses a risk of collision. For example, microwave system, i.e., radar, are relatively costly to manufacture, tend to pollute the environment over the electromagnetic spectrum if utilized on a wide spread basis and have limited ability to control the directivity of the beam energy to reasonably sized detection areas. The electrostatic membrane transducers used in ultrasonic systems for coupling energy to and from the air are fragile and present a risk of being damaged in a road environment. Moreover, the piezoelectric ceramic devices used in ultrasonic systems possess poor energy coupling efficiency and therefore cannot provide the target sensing range that is required in many road vehicular applications.
The problems mentioned above are exacerbated by the diverse types of environmental conditions and terrain under which vehicles are normally used. Objects or features such as highway signs, curbs and line markings on the pavement may give rise to false detection signals. On the other hand, weather conditions involving rain, snow, fog, etc. may impair the effective "vision" of the collision avoidance system to the point that it is unable to detect objects or vehicles posing a risk of collision. Further, in order to reliably detect objects or vehicles posing a risk of collision, it is necessary to define with some degree of precision the zone intended to be monitored. One zone that is of particular interest is that normally referred to as the vehicle operator's "blind spot." An operator's blind spot will, of course, vary from vehicle to vehicle. In some cases, the vehicle operator is unable to detect the presence of an object or vehicle in the blind spot, either due to his line of sight being physically blocked or an inability to view the area within the blind spot by means of mirrors or the like. In other applications, the blind spot may comprise a relatively substantial area, as in the case of large tractor-trailer vehicles. In these applications, various types of sophisticated mirror systems have been devised so that the operator may view most if not all of the area within the blind spot; however, these systems employ multiple mirrors, and it may be quite difficult for the operator to quickly view all of these mirrors in order to see all portions of the blind spot area before he executes a change of lanes. Moreover, some of these mirrors are convex or horizontal in configuration which actually distort the view by altering the apparent range and/or orientation of the scene.
Complicating the problems mentioned above is the fact that vehicle operators sometime become lackadaisical in using the normal means available to them for areas within or adjacent to the blind spot. An operator may easily overlook the presence of a small object or vehicle, such as a bicycle or motorcycle within the blind spot, if he merely quickly glances at his sideview or rearview mirrors.
The present invention is directed to overcome all of the deficiencies mentioned above.